Date of Award
Doctor of Philosophy (PhD)
Materials Science and Engineering
Dr. Igor Luzinov
Dr. Olga Kuksenok
Dr. Phil Brown
Dr. Raj Bordia
Growing environmental concerns associated with the production and disposal of traditional plastics, the depletion of non-renewable fossil resources, as well as pollution of landfills and the oceans have motivated researchers to pursue alternatives to petroleum-based materials. To this end, this research aims to develop environmentally friendly alternatives to petroleum-based plastics, thereby reducing the dependence on non-renewable resources. Namely, we report on the fabrication and characterization of polymer blends consisting of copolymers derived from soybean oil (as a minor phase) and matrix made from commercially available polymers: Polystyrene (PS) and Poly(lactic acid) (PLA). The copolymers employed in this work were obtained by free radical emulsion copolymerization of high oleic soybean monomer (HOSBM) with Myrcene and Styrene (ST).
First, the copolymer composed of HOSBM and Myrcene (90:10 wt/wt) was blended with PS in the range of 5-20% to harness the favorable properties of PS while improving the material’s ductility and toughness. The blends depicted phase-separated morphology and were partially miscible. However, improvement in toughness and ductility was not achieved, and when compared to mechanical models, the experimental moduli fell below the lower-bound moduli predicted by the Takayanagi model.
To improve the interfacial stress transfer, a chemical modification was made to the copolymer composition, thereby replacing Myrcene with an equal amount of Styrene (ST) to obtain HOSBM-ST (90:10 wt/wt). The PS/HOSBM-ST (90-10) blends also had a phase-separated microstructure with partial miscibility. The employment of HOSBM-ST (90-10) in the blends at 5-20% improved the interfacial stress transfer, and the experimental values of the moduli were close to the upper bound values predicted by the Takayanagi model. The optimal HOSBM-ST (90-10) loading where the relatively high modulus and strength (2302, 37 MPa) were complimented with improved ductility and toughness (0.027 mm/mm, 0.660 MJ/m3) , was 10%. The improvement of the mechanical properties compared to the blends containing HOSBM-Myrcene (90-10) came at the cost of reducing the bioderived content of the copolymer. Thus, the reduction of Styrene content in the HOSBM-based copolymer from 10 wt% to 5 wt% was explored and the effects on the properties of the blends were investigated. The phase-separated and partially miscible PS/HOSBM-ST (95-5) blends showed similar thermal and mechanical behavior to those containing the same amount of HOBSM-ST (90-10). However, the blend consisting of 5% HOBSM-ST (95-5) demonstrated the highest modulus and strength (2503, 43 MPa) as well as ductility and toughness (0.031 mm/mm, 0.920 MJ/m3) among all PS-based blends studied here.
The blending of HOSBM-Myrcene (90-10) with PLA was also investigated with the aim of obtaining fully bioderived polymer blends with high modulus/strength and improved toughness/ductility compared to the brittle PLA. The copolymer was added at 5-10% loadings to harness the high modulus and strength of PLA. The blended materials were partially miscible, and had high modulus and strength (2675, 54 MPa for 5% HOSBM-Myrcene (90-10) addition) as well as improved ductility and toughness (0.120 mm/mm, 5.53 MJ/m3 for 5% HOSBM-Myrcene (90-10) addition). The water absorption and wettability of PLA were also significantly decreased with the addition of the hydrophobic plant oil-based copolymer.
Mhesn, Najah, "Fabrication And Characterization of Polymer Blends Containing Plant Oil-Derived Copolymers" (2022). All Dissertations. 3200.
Available for download on Sunday, December 31, 2023